VASOPRESSIN VIA RECEPTOR-STIMULATED PHOSPHOLIPASE-D - DIFFERENTIAL REGULATION OF TRANSPHOSPHATIDYLATION AND PHOSPHOLIPID HYDROLYSIS BY PROTEIN-KINASE-C

Phospholipase D belongs to a group of membrane associated phospholipas es which have been shown to be activated by G-protein coupled neurotra nsmitter receptors. Phosphatidylcholine is the primary substrate for p hospholipase D generating phosphatidic acid (PA) and choline. In the p resence of 1% ethanol, phospholipase D catalyzes a transphosphatidylat ion reaction generating phosphatidylethanol (PEt) which is an indicato r of phospholipase D activation. In the present study, we utilized Chi nese hamster ovary (CHO) cells stably transfected with and expressing a rat V1a vasopressin receptor to study the regulation of phospholipas e D by protein kinase C and calcium. Arginine-vasopressin (AVP) stimul ated the release of H-3-PEt and H-3-PA in cells pre-labelled overnight with 3H-palmitic acid. The phorbol ester, phorbol 12-myristate 13-ace tate (PMA), stimulated the release of PEt and PA that was additive wit h AVP over 15 min. However, long-term stimulation with PMA, which dese nsitizes protein kinase C, decreased PEt production while simultaneous ly increasing PA production. Differential regulation of PEt and PA pro duction by PMA suggests the existence of more than one phospholipase D isoenzyme. Though differentially regulated by protein kinase C, both AVP-stimulated PEt and PA production required extracellular and not in tracellular calcium.